Killing Agent Research Articles

Pest interactions and canopy gaps in ponderosa pine stands in the Black Hills, South Dakota, USA

Gap frequency and size, cause (predisposing factors, killing agents, and tree response), and coarse woody debris composition (snags and downed logs) were assessed in three stands differing in management history. Disturbance agents were usually coupled concurrently and sequentially. A qualitative model (relational diagram) developed to display these interactions and the activity distributed among different disturbance pathways suggests that management activity (1) diminishes pest-caused structural diversity in the forest ecosystem, (2) decreases functional diversity associated with interacting diseases, insects and other disturbance agents, and (3) alters the abundance and decomposition distribution of dead wood.

Hyperthermic therapy for HIV infection

The objective of this paper is to review what is known about the antiviral effects of fever and to highlight the scientific evidence supporting the hypothesis that hyperthermic therapy may prove to be a beneficial treatment modality for persons infected with HIV. Our hyperthermic hypothesis is based upon the mutant escape, quasispecies theory of HIV antigenic diversity. We propose that, if initiated during the asymptomatic stage of HIV infection, hyperthermia may prove to decrease the number of mutant HIV strains arising due to evolutionary pressures created by the patient's immune system, with a resultant prolongation of the asymptomatic period of infection. A review of the literature from three areas of investigation: the immune response to fever, heat as a tumor killing agent, and preliminary studies with fever and retroviral infections, strongly suggests that there is a good scientific basis for the use of hyperthermic therapy in a multimodal treatment approach to HIV infection.

Development of TiO x-bearing steels with superior heat-affected zone toughness

TiO x steels with superior toughness of the heat-affected zone (HAZ) and applicable to a wide range of welding heat inputs have been developed using advance metallurgical techniques. A promising practice in industrial production is adopting a Ti-killing process in which ferro-titanium alloys are utilized as killing agents in an Al-free molten steel. This process creates Ti-oxides with various crystalline structures (referred to as TiO x) in a steel matrix. These TiO x inclusions improve the toughness of coarse-grained HAZ by promoting the formation of intragranular acicular ferrite (IAF), which can section an austenite grain into several colonies and refine the effective grain size to fracture resistance. The volume fraction of IAF is closely related to the number of TiO x inclusions, inclusion diameter, austenite grain size and the hardenability of steels. The favourable conditions for the formation of IAF and the concept of process control are discussed.

Evaluation of the flushing out activity of pyrethroids on Triatoma infestans

Tetramethrin, deltamethrin and Cypermethrin formulated as fumigant tablets or spray(ing) solutions showed flushing out activity on Triatoma infestans. Fumes arising from the tablets were analysed by gas chromatography. The proportion of pyrethroid liberated was between 10 and 20% of the original amount formulated. The flushing out activity shown was dependent on the pyrethroid compound, insect stage and sex. In general deltamethrin proved the most active flushing out agent and Cypermethrin the least active. Maximal activity was shown in the combination of nymphs and tetramethrin. Nymphs of Rhodnius prolixus were only flushed out by deltamethrin. In all cases, deltamethrin and Cypermethrin yielded 100% mortality 7 days after exposure to the pyrethroid fumes, while tetramethrin was not a killing agent.

The role of reactive oxygen species in the killing of the bacterial fish pathogen Aeromonas salmonicida by rainbow trout macrophages

The role of reactive oxygen species (ROS) in the killing of the bacterial pathogen Aeromonas salmonicida by in vitro cultured rainbow trout (Oncorhynchus mykiss) head kidney macrophages has been investigated. Using a microtitre plate bactericidal assay the respiratory burst pathway responsible for ROS generation was inhibited completely using the NADPH oxidase inhibitor trifluoperazine and partially by the use of ROS scavengers (formate and/or mannitol) and the antioxidative enzymes SOD and/or catalase. Increased bacterial survival of an avirulent strain (MT004) in the presence of trifluoperazine, catalase and formate confirmed that ROS such as hydrogen peroxide and hydroxyl radicals were indeed an important killing agent. This was further confirmed using sodium nitroprusside and aminotriazole, inhibitors of SOD and catalase respectively. The presence of aminotriazole caused a significantly increased bactericidal activity against a virulent strain (MT423) normally resistant to killing by cultured resident rainbow trout head kidney macrophages.

Cytotoxic proteins.

Cytotoxic proteins, which enter eukaryotic cells and catalytically inactivate protein synthesis, are being increasingly studied using a combination of molecular biology, cell biology and structural approaches. The creation of genetically engineered fusions with alternative cell-binding ligands paves the way for tailor-made, cell-type-specific killing agents.

Activity of antibiotics againstStaphylococcus aureus within polymorphonuclear neutrophils

The intracellular location of certain strains of Staphylococcus aureus serves as a reservoir of bacteria which is thought to be important in therapy of recurrent infections in humans and in chronic staphylococcal mastitis in dairy cows. This overview summarizes data pertaining to the intracellular survival of Staphylococcus aureus within polymorphonuclear neutrophils (PMNs) both in vitro and in vivo in the face of antibiotic treatment. While compounds such as rifampin, clindamycin, erythromycin, and ciprofloxacin have been shown to be rapidly taken up by PMNs, the ability of antibiotics to concentrate within PMNs did not strictly correlate with their ability to kill intracellular Staphylococcus aureus. Rifampin and ciprofloxacin have been shown to be the most effective intraphagocytic killing agents, while clindamycin and erythromycin were inactive in these in vitro assays. In vivo, in therapy of Staphylococcus aureus arthritis and peritonitis in humans and in certain mouse models rifampin has generally been shown to be more effective than comparator antibiotics. In a staphylococcal subcutaneous abscess model, however, clindamycin was very effective in curing the Staphylococcus aureus abscesses in this system where PMNs were the primary inflammatory cells involved. The intracellular bacterial counts decreased as rapidly as the extracellular bacteria. Rifampin was also effective in the abscess model but ciprofloxacin was ineffective at the highest doses tested. The relevance of in vitro and in vivo models and the importance of PMNs as a reservoir of infection in staphylococcal diseases in humans and the dairy cow are discussed.

Pengaruh ammonia sebagai “killing agent” pada pengecatan bulu kulit kelinci

The objective of this research is to find out the effluence of ammonium hydroxide as killing agent to the uniformity and fintness of the colour of rabbit fur after dyeing. This research made use of 27 pieces of green salted rabbit skin having white colour. In killing process the rabbit fur was treated recpectively in a liquar of 10, 15 and 20 cubic centimetres of ammonium hydroxide of 22% strength in one litre of water, furthermore the fur was dyed. The dyed fur was visually examined for the uniformity and fitness of the colour of the dyed fur, and physically tested for the rub fastness of the dye. The highest value of rub fastness achieved by the dyed rabbit fur treated in 20 cubic centimetres of ammonium hydroxide in one litre of water. It advisable to use 20 cubic centimetres of ammonium hydroxide of 22 % strength in one litre of water as killing agent in rabbit fur dyeng process.

SUSCEPTIBILITY OF THE MIGRATORY GRASSHOPPER, MELANOPLUS SANGUINIPES (FAB.) (ORTHOPTERA: ACRIDIDAE), TO BEAUVERIA BASSIANA (BALS.) VUILLEMIN (HYPHOMYCETE): INFLUENCE OF RELATIVE HUMIDITY

AbstractIn laboratory tests, Melanoplus sanguinipes (Fab.) was susceptible to infection by Beauveria bassiana (Bals.) Vuillemin conidia. Infection occurred independently of the relative humidity (RH) (12, 33, 76, 100% RH). No significant difference was observed in the final percentage mortality of the treated grasshoppers and in the lethal times (LT50)(P > 0.05) under the RH conditions studied. However, the daily rate of mortality after treatment was higher at 76% RH than at 33% RH. High natural mortality occurred at 100% RH.At 100% RH, treatment with B. bassiana was associated with an outgrowth of microorganism that created septicemic conditions in the absence of the characteristic symptoms of mycosis. Below 100% RH, mycelial growth on cadavers was never observed, even though partial or total insect mummification occurred, and a pink body coloration on approximately 80% of the insects indicated Beauveria as the killing agent. Once transferred to 100% RH, no more than 5% of the treated grasshoppers exhibited external mycelial growth.The microenvironment at the cuticular level of the grasshopper allows expression of conidial pathogenicity regardless of ambient RH. Hence, together, these observations suggest the feasibility of field testing with B. bassiana as a bioinsecticide against M. sanguinipes in semi-arid climatic areas.

11] Use of tritium-labeled precursors to select mutants

A killing selection is certainly a method of choice for rapid mutant isolation. However, it is very often difficult to meet the “comfortable” situation of having, for selection, a toxic compound analogous to an intermediate in the pathway of interest. This chapter illustrates with four examples that the use of tritiated-labeled precursors overcomes this difficulty and provides a powerful and general method of selection for mutants defective in membrane transport and in metabolic pathways. With these four examples of tritium suicide selection, the chapter shows that it is possible to devise a selection procedure allowing mutant isolation in a reasonable time period with either metabolizable or nonmetabolizable precursors. The tritium suicide has several advantages and is called “radiosuicide,” and was first used with bacterial genetics. This method is highly selective as the substrate itself of the pathway to “mutate” is the killing agent. The principle is based on the killing effects generated by the radiolytic decay of the incorporated labeled precursor. A killing selection is certainly a method of choice for rapid mutant isolation. However it is very often difficult to meet the “comfortable” situation of having, for selection, a toxic compound analogous to an intermediate in the pathway of interest.

10] Suicide selection of mammalian cell mutants

Publisher Summary This chapter describes suicide selection of mammalian cell mutants. The principle of suicide selection of mutant cells was used in microbial genetics prior to its application to mammalian somatic cells. In this procedure, a population of cells, most of which display wild-type growth characteristics and a few rare ones with additional mutant nutritional requirements, is placed in a selective medium in which the former but not the latter can grow. An agent that will kill growing cells is then added. Bromodeoxyuridine- (BrdUrd-) visible light used as the killing agent to isolate different mutants. The chapter describes the standard “BrdUrd-light” protocol and discusses the parameters that may require adjustment for particular cell types and applications. This procedure depends on the differential incorporation of the thymidine analog, bromodeoxyuridine (BrdUrd), into the DNA of growing but not into nongrowing cells in selective conditions sufficient for growth of wildtype but not mutant cells. After incorporation of BrdUrd, the cell culture is exposed to “visible light,” a component of which in the range of 313 nm results in photolysis of BrdUrd-containing DNA and death of wild-type (growing) but not mutant (nongrowing) cells.

Accumulated Dead Insects and Killing Agents Reduce Catches of Spruce Budworm (Lepidoptera: Tortricidae) Male Moths in Sex Pheromone Traps

Coating the inside of sex pheromone-baited funnel traps with insect trapping adhesive resulted in doubling of the catch of male spruce budworm, Choristoneura fumiferana (Clemens). This result suggests that half the moths entering funnel traps escape. Dichlorvos-impregnated resin strips and a mixture of ethanol and ethylene glycol used as killing agents in nonsticky traps had a repellent effect; consequently, catches were reduced. Presence of dead moths in the traps also reduced catches.

Effect of Pyrethroids on Knockdown and Lack of Coordination Responses of Susceptible and Resistant Diamondback Moth (Lepidoptera: Plutellidae)

Among DDT and the 10 pyrethroids tested, permethrin, cypermethrin, deltamethrin, and fenvalerate were most toxic against a field strain of Plutella xylostella (L.) that had high levels of resistance to all insecticides tested. Knockdown effect of these compounds against larvae and adults of susceptible and resistant strains was evaluated by a residual-film method. Symptoms of poisoning are described. When larvae or adults could no longer stand and had to lie on their sides, they were considered knocked down. Pyrethroids with primary alcohol esters produced more acute symptoms than those with secondary alcohol esters. Responses of resistant larvae and adults were less pronounced than those of susceptible ones. In the resistant strain, addition of synergist piperonyl butoxide (PB) to the pyrethroids produced symptoms displayed by the susceptible strain. Tetramethrin, which was not highly toxic, was the most potent knockdown agent against susceptible larvae. Knockdown action of all pyrethroids appeared much more slowly in resistant larvae; fluvalin ate and flucythrinate were least effective as knockdown as well as killing agents. Addition of synergists PB, S,S,S-tributyl phosphorotrithioate, and chlordimeform generally enhanced knockdown action of most pyrethroids in resistant larvae, but had only limited effect in susceptible larvae. Maximal knockdown of adults by fenvalerate was reached 60–90 min after exposure; PB synergized this action of fenvalerate and reduced recovery of the moths within 24 h.

Laboratory Evaluation of Permithrin in the Nomate Attract N‘ Kill Formulation for Pink Bollworm Control, 1983

Abstract Permithrin used as the killing agent in the Nomate Attract n‘ Kill formulation was tested at the recommended field rate of 4.45 g (AI)/ha and at 0.5, 2, 4, 6, and 8 times the recommended field rate for pink bollworm control. Tests were conducted in 2 plexiglass wind tunnels 61 x 61 cm x 244 cm long. Forty cotton terminals were cut from potted plants maintained in a greenhouse. The stem of each terminal was placed in a 19 X 70 mm glass vial filled with a nutrient solution. Twenty of the vialed terminals were placed in a 4 X 5 grid on the upwind end of each tunnel. The plant grid covered approximately 1 square m on each tunnel floor. Two plant terminals in each tunnel were randomly selected, and a leaf on each was treated with .03 g of Biotac 3 or a Biotac 3:Biotac 19 combination mixed with one of the 6 Permithrin rates tested. The 2 highest rates were mixed with blends of Biotac 3 and 19 to maintain a viscosity similar to the commercial product. An 8 mil Nomate fiber was attached to each treatment site. Controls were identical except no Permithrin was added to the Biotac.

Bactericidal and cytotoxic effects of hypothiocyanite-hydrogen peroxide mixtures.

Lactoperoxidase catalyzes the oxidation of thiocyanate by hydrogen peroxide into hypothiocyanite, a reaction which can protect bacterial and mammalian cells from killing by hydrogen peroxide. The present study demonstrates, however, that lactoperoxidase in the presence of thiocyanate can actually potentiate the bactericidal and cytotoxic effects of hydrogen peroxide under specific conditions, such as when hydrogen peroxide is present in the reaction mixtures in excess of thiocyanate. The toxic agent was also formed in the absence of lactoperoxidase in a reaction between hypothiocyanite and hydrogen peroxide. Sulfate, sulfite, cyanate, carbonate, and ammonia, which have been postulated to be formed in the chemical oxidation of hypothiocyanite by hydrogen peroxide, were not bactericidal and did not potentiate the bactericidal effect of hydrogen peroxide. Cyanosulfurous acid, the only other postulated product of the chemical oxidation of hypothiocyanite by hydrogen peroxide, may be the killing agent.

Field evaluation of chemical attractants against the flyFannia femoralis (Diptera: Muscidae)

Four chemical compounds previously shown to be attractants toHippelates eye gnats and houseflies were evaluated againstFannia femoralis (Stein). Two of the compounds, trimethylamine hydrochloride andn-butyric acid, were determined to be the principal attractants against this fly. A composition containing trimethylamine hydrochloride (yielding trimethylamine in presence of water),n-butyric acid, and an anchovy meal inert carrier proved highly attractive. To evaluate the practical use of the synthetic fly attractant (SFA) formulation, a large-scale trial over an entire poultry ranch was implemented using SFA formulation and a sugar toxicant (as a killing agent) in specially designed traps. Within 2 weeks after initiation of SFA-toxicant treatments, significant reduction inF. femoralis population from the pretreatment level occurred. This high level of reduction prevailed during the remainder of the treatment period.

Univalent antibodies kill tumour cells in vitro and in vivo.

Antibody molecules are bivalent, or less often multivalent, with each antibody site within a single molecule having the same specificity. Bivalency must enhance the tenacity of antibody attachment to cell surfaces, as dissociation will require simultaneous release at both sites. However, the bivalency of the antibody sometimes induces a target cell to undergo antigenic modulation1–3, thereby offering the cell a means of evading complement and the various effector cells recruited by the antibody. We have investigated the attack by univalent antibodies, which, despite removal of one antibody site, retain their Fc zones and hence their ability to recruit the killing agents, on neoplastic B lymphocytes of the guinea pig L2C line. Rabbit antibodies raised against surface immunoglobulin of these cells were partially digested with papain to yield the univalent Fab/c derivatives4,5. We report here that these derivatives showed enhanced cell killing both in vitro and in vivo, and that this enhancement appeared to derive from avoiding antigenic modulation.

Killing of bacteria with electric pulses of high field strength.

Bacteria of the type E. coli K12 have been treated in experiments using high-voltage pulses of short time (microseconds) as a killing agent. The role of different experimental parameters has been studied: kind of electrolyte, concentration, length of pulses, field strength, pH and temperature. Electrolytes with bivalent cations were found to reduce the lethal action. the relative rate of killed bacteria was shown to be mainly governed by the field strength and the treatment time, which is defined by the product of pulse number and decay time constant. From the obtained results a function has been developed which enables the precalculation of the killing rate for E. coli, provided that certain limits of experimental conditions are considered. No correlation between the applied electric energy and the lethal effect could be found.

Primary Lysosomes of the Ciliate Pseudomicrothorax dubius: Cytochemical Identification and Role in Phagocytosis*

SYNOPSIS. Filamentous cyanobacteria are ingested through the cytopharynx of the ciliate Pseudomicrothorax dubius. The cytopharynx is a complex of microtubules and microfilaments located in a highly vesiculated cytoplasm, the phagoplasm. Two types of membrane‐bounded phagoplasmic vesicles can be distinguished by their differences in size, fine structure, and acid phosphatase (AcPase) content. One type has a homogeneous, electron‐dense interior which is AcPase‐positive. These vesicles are present in fed cells and in unfed cells devoid of food vacuoles, and thus appear to be primary lysosomes. During phagocytosis, exocytosis within the cytopharynx of the primary lysosomes results in the elaboration of a food vacuole. The vacuole grows by incorporation of lysosomal membrane; lysosomal hydrolases are liberated into the vacuole. Within less than 1 second of AcPase's entry into the food vacuole, it is detectable within the cyanobacterial cytoplasm, and within 5 seconds, destruction of the cyanobacterial filament is observed. It is hypothesized that the rapidity of hydrolase penetration of the cyanobacterial cell wall is the result of the action of molecules analogous to the “killing agents” of neutrophil leukocytes, which rapidly render bacterial envelopes permeable. AcPase, and presumably other hydrolases, are present in the cyanobacterial filament when filament destruction occurs; they thus appear implicated in this process. Hydrolases may activate an autodestruction mechanism in the cyanobacterium. Firm adherence of the food vacuole membrane to the cyanobacterial filament is demonstrated, and its role in phagocytosis is discussed.

The activity of some pyrethroids against Periplaneta americana and Blattella germanica

AbstractThe knockdown and contact killing actions of various pyrethroids were compared using Blattella germanica and Periplaneta americana. A wide range of knockdown activity was found; 5‐benzyl‐3‐furylmethyl (1R)‐cis‐3‐(dihydro‐2‐oxo‐3‐thienylidenemethyl)‐2,2‐dimethylcyclopropanecarboxylate (RU 15525) acted fastest, more rapidly than pyrethrins, against B. germanica as well as having a low LD50 value. Topical application and direct spray tests showed that (S)‐α‐cyano‐3‐phenoxybenzyl (1R)‐cir‐3‐(2,2‐dibromovinyl)‐2,2‐dimethylcyclopropanecarboxylate (NRDC 161) was more active as a killing agent, by an order of magnitude, than cismethrin, the next most active compound, and also had considerable knockdown activity. Piperonyl butoxide generally had little synergist effect. Female P. americana were over three times more tolerant than males to a range of insecticides applied topically. Residual knockdown action in the WHO resistance test was observed to provide baseline data. There was little overlap in speed of action between pyrethroids and other insecticides among the compounds tested.